It is known that sterilization must occur at a temperature which is as high as possible, but yet below a temperature at which there is a risk of damage to the packaging material of the objects to be treated. One example of such goods with packaging material is pharmaceutical products constituting plastic ampoules, such as polypropylene, which has a comparatively low temperature at which softening compounds in the plastic start to diffuse out of the material. In the hottest part of a packaging, which is not in contact with the liquid in the package, the plastic will start shrinking and may become deformed, and cracks may appear. This situation cannot be tolerated with respect to the risk of bacteria growing into the cracks. Therefore, it is a highly desirable object to use the highest possible temperature in the chamber without reaching a temperature which would damage the material in ordder to properly sterilize the packaged product.
Autoclaves for sterilization of products in packages are known but cannot be considered as satisfactory since it is not possible during the sterilization period in these autoclaves to regulate pressure and temperature in the autoclave chamber with such accuracy that the treatment temperature in fact can be kept near the temperature determined by the tolerance of the packaging material. Therefore, a lower temperature than desired is chosen, with the consequence that the sterilization treatment times are very long. On the other hand, if a high temperature is chosen there is the risk of some packaging material being destroyed during the treatment, and as a result the outcome of the treatment has to be carefully controlled.
These known systems for sterilization of objects are based on an intermittent supply to the chamber of the media controlling the process with respect to given criteria. The control of the supply of one of these media is entirely independent of the supply of the other medium and thus, the periods of supply of the media will be upset. For example, this can result in that if the chamber temperature is sufficiently high there will be no supply of steam, so that the pressure will drop and cold compressed air will be supplied. If instead the temperature is too low, but the pressure sufficiently high, only steam will be supplied to the chamber. This steam will enter the system with the total pressure of the entire chamber against it. Due to the character of the control, temperature gradients can appear in the system and even locally in the chamber, because of the impossible task of designing a symmetrical pipe system for affluence and effluence of the chamber. Furthermore, distribution of the temperature gradients to certain locations in the chamber tends also to be dependent on the charge of the autoclave. Considerable research has been undertaken to master this problem, especially after delivery and on trimming of a new plant it has been necessary to spend much work on attempts to achieve improvements. This work has, among other things, included re-dimensioning of the pipe system, particularly in the chamber.
It would be evident from the foregoing that an object of the present invention is to provide a thermodynamic system which can be controlled with great accuracy and permits a constant temperature to be maintained in the entire chamber. Thus, the invention makes it possible to accomplish a given process in this system.
Another object of the present invention is to provide a system which is easy to trim for operation with certain parameter values for a given program or to readjust the system for operation with another program.
A further object of the present invention is to provide a method of achieving a thermodynamic system which can be controlled with great accuracy and maintains a constant temperature in the entire chamber and which the chamber with products therein is heated, after which the working media are caused to flow through the chamber in quantities controlled by regulating valves that are operated by means controlled by the temperature in the steam conduit, and by the pressure and the temperature in the chamber.
Still another object of the present invention is to provide a device for carrying out the method according to the invention and is mainly characterized in that a regulating valve in the steam supply conduit is operated by a regulator controlled by the temperature in the conduit after the valve, while a regulating valve in the air supply conduit is operated by a regulator controlled by the temperature in the chamber. Moreover, the device is provided with a bypass conduit with a valve that is arranged in the compressed air supply conduit, the valve of the bypass conduit being operated by a pressostat controlled by the pressure in the chamber. Furthermore, the vent conduit and the discharge conduit each have a throttle for constant flow therethrough, and the vent conduit further has a valve operated by a regulator controlled by the pressure in the chamber.